Circuit breaker with reverse override device

ABSTRACT

A circuit breaker characterized by a pair of contacts operable between open and closed positions and a circuit breaker mechanism releasable to effect opening of the contacts. The mechanism comprising a trip structure and including a trip rod, a crank shaft structure, and associated closing spring means operable to close the pair of contacts, manual trip means operatively connected to the trip rod for tripping the mechanism and comprising a trip member movable between tripped and untripped positions and biased in the untripped position. The crank shaft comprising a cam operable for holding the trip member in the tripped position when the contacts close against a heavy fault current.

United States Patent Patel CIRCUIT BREAKER WITH REVERSE OVERRIDE DEVICE Nagar .1. Patel, Pittsburgh, Pa.

Westinghouse Electric Corporation, Pittsburgh, Pa.

Filed: June 14, 1973 Appl. No.: 370,080

Inventor:

Assignee:

US. Cl. 200/153 SC, 335/46 Int. Cl. H01h 3/30, H01h 3/42 Field of Search..... 200/166 H, 153 SC; 335/46,

References Cited UNITED STATES PATENTS 3/1971 l-lauser 200/153 SC 6/1971 Bould et al. 335/190 Primary Examiner-Robert K. Schaefer Assistant Examiner-William .1. Smith Attorney, Agent, or Firm-L. P. Johns [5 7] ABSTRACT A circuit breaker characterized by a pair of contacts operable between open and closed positions and a circuit breaker mechanism releasable to effect opening of the contacts. The mechanism comprising a trip structure and including a trip rod, a crank shaft structure, and associated closing spring means operable to close the pair of contacts, manual trip means operatively connected to the trip rod for tripping the mechanism and comprising a trip member movable between tripped and untripped positions and biased in the untripped position. The crank shaft comprising a cam operable for holding the trip member in the tripped position when the contacts close against a heavy fault current.

5 Claims, 4 Drawing Figures PATEMIE' :m 1 91974 PATENTE, xsv 1 91974 SHEET 2 BF 3 NOE CIRCUIT BREAKER WITH REVERSE OVERRIDE DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to circuit breakers, and more particularly, to a trip device which saves the breaker from hammering itself to destruction if it attempted to close against fault currents that are higher than the ability of the breaker to close and latch.

2. Description of the Prior Art When a circuit breaker closes against heavy fault currents, higher than the ability to close and latch, the resulting blow-off forces cause the movable contacts to reverse and charge the closing springs. As the springs are charged, they attempt to reclose the breaker repeatedly. One answer to the problem is to provide closing springs strong enough to overcome the blow-off forces and thereby maintain the breaker in the closed position once the closing action is begun. However, certain disadvantages are incurred where very heavy closing springs are used and include excessive hammering of the contacts at normal currents. Another disadvantage is that existing housings for circuit breakers cannot accommodate the larger, more powerful springs. Finally, inasmuch as heavy fault currents occur infrequently, it is not economical to seriously consider the use of heavy closing springs.

SUMMARY OF THE INVENTION It has been found in accordance with this invention that the foregoing problem may be overcome by providing a circuit breaker having a pair of contacts operable between open and closed positions, a circuit breaker mechanism releasable to effect opening of the contacts, a trip structure for latching the circuit breaker mechanism in the closed position and for releasing the circuit breaker mechanism, the trip structure comprising a trip rod operatively connected to the circuit breaker mechanism, a crank shaft structure operable to close the pair of contacts, closing spring means connected to the crank shaft structure, manual trip means operatively connected to the trip rod for tripping the mechanism and comprising a trip member movable between tripped and untripped positions and biased in the untripped position, a cam on the crank shaft and operable for holding the member in the tripped position when the contacts bounce as a result of attempt to close against fault currents higher than the ability of the breaker to close and latch, the latch means comprising a pin mounted on the trip member and extending into the path of rotation of the earn, the member comprising a substantially vertical slot and the pin being slidably movable in the slot, and the pin being movable to a retracted position in the slot when the closing spring means are being charged.

The advantage of the device of this invention is that when fault currents occur above the ability to close and latch, the circuit breaker is prevented from destroying itself due to repeated closing efforts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an end view, with parts broken away, of a circuit breaker;

FIG. 2 is a vertical sectional view taken generally along the line 11-" of FIG. 1;

FIG. 3 is a vertical sectional view taken on the line IIIIII of FIG. 1; and

FIG. 4 is a view similar to FIG. 3, illustrating the parts in alternate positions.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, there is shown in FIGS. I and 2 a three-pole circuit breaker 5 comprising a housing structure 7 and a circuit breaker structure 9 supported on the housing structure 7. The circuit breaker 5 is more specifically described in US. Pat. No. 3,590,192, issued June 29, 197].

As shown in FIG. 2, the circuit breaker structure 9 comprises a stationary contact I1 and a movable contact 13 for each pole unit of the three-pole structure. Each of the movable contacts 13 is supported on a conducting contact arm 15 that is pivotally supported on a terminal conductor 17 by support means 19. An insulating connecting member 21 is pivotally connected at one end to the contact arm 15 and at the other end to a lever 23 that is welded on a common jack shaft or tie bar 25. The jack shaft 25 (FIG. 1) extends across all of the poles of the circuit breaker and a separate lever 23 for each pole unit welded on the jack shaft. A stored-energy spring closing mechanism 27 which is operable for closing the contacts 13 and II includes a pair of closing tension springs 29 which actuate a pair of crank arms 30 which are fixedly mounted on a crank shaft 31.

As shown in FIG. 2, the circuit breaker is in the contact-open position with the stored-energy closing springs 29 in the charged condition. The movable ends of the springs 29 are mounted on spring support pins 33. A trip structure 35 is provided for latching the circuit breaker structure 9 in the closed position and for releasing the circuit breaker from the open position. For that purpose, the trip structure 35 includes a trip shaft 37, a trip latch 39, a link 41 and a fixed pivot 43 on which the link is mounted. Other means are provided to close the contacts 11, 13 which means include a holding pawl 44, that is rotated either by spring release armature 46, or by pushing CLOSE button 48 to allow the closing springs 29 to discharge and close the breaker. The breaker remains closed because the trip latch 39 is restrained from counterclockwise rotation by the trip shaft 37. The breaker can be tripped by pushing the trip lever 47 shown in FIG. 3.

In accordance with this invention, the circuit breaker 5 is provided with a reverse override device which, as shown in FIGS. 1, 3 and 4, prevents recharging of the closing springs 29 when the breaker bounces open due to its attempt to close against fault currents higher than its close and latch ability. In FIG. 1 a manual trip handle 47 is provided on a trip member 49. The trip member 49 is supported in place on a mounting bracket 59, the upper end of which is attached to the housing structure 7. Mounting pins 53 extend from the mounting bracket and through slots 55 on the trip member 49. The member 49 includes a projection 57 extending from the underside thereof, which projection in turn is provided with an intumed flange 59, the inner end of which is adapted to engage a trip arm 61 extending from the trip handle 37. Accordingly, when the trip handle 47 is manually moved to the right, as viewed in FIG. 3, the flange 59 rotates the trip shaft 37.

In addition, a downturned flange 63 extends from the inturned flange 59 and includes a vertically extending slot 65 (FIG. 4) in which a pin 67 is vertically'movably mounted. A cam 69 is fixedly mounted on the crank shaft 31 and the cam includes a step surface or edge 71. When the crank shaft 31 is rotated counterclockwise during the charging operation of the springs 29, the pin 67, which extends into the path of travel of the cam 69, rides on the peripheral surface thereof by moving vertically in the slot 65. When the closing springs 29 are fully charged, the pin is on the high portion of the cam 69 (FIG. 4) where it remains so'long as the springs are in the charged condition.

In FIG. 3, the circuit breaker is in the process of closing and the crank shaft 31 has turned the cam 69 counterclockwise far enough to move the step surface or edge 71 to the left beyond the pin 67, which in turn, drops in the slot 65. As the breaker closing motion continues, the pin 67 falls to the lower edge of the step surface 71 and remains there. When the breaker contacts 11, 13 approach the closed position under a condition of excessive fault currents, magnetic forces incurred by the ensuing current between the contacts become sufficiently great to exceed the force of the closing springs 29 and blow the contacts back to the open position, thereby rotating the closing mechanism 27 in the reverse direction. In other words, the mechanism 27 rotates clockwise until the step surface 71 of the cam 69 engages the pin 67 and moves the push-to-trip member 49 to the right in order to once again upset the trip shaft 37. With the trip shaft 37 upset in the tripped position, the closing springs discharge harmlessly without moving contacts 13.

As the push-to-trip member moves against the trip arm 61, the combined movements of the member and the cam cause the pin 67 to move upwardly in the slot 65 where it remains on the curved periphery of the cam. Inasmuch as the trip shaft 37 is upset, it holds the circuit breaker in the trip-free position, allowing the springs to discharge harmlessly.

In summary, the device of this invention overcomes the problem of a circuit breaker destroying itself due to repeated closing efforts against fault currents beyond its close and latch ability which may occur in an electric circuit from time to time.

What is claimed is:

1. A circuit breaker comprising a pair of contacts operable between open and closed positions, a circuit breaker mechanism releasable to effect opening of said contacts, a trip structure for latching the circuit breaker mechanism in the closed position and for releasing said circuit breaker mechanism, said trip structure comprising a trip shaft operatively connected to said circuit breaker mechanism, a crank shaft structure operable to close said pair of contacts, closing spring means connected to said crank shaft structure, manual trip means operatively connected to said trip shaft for tripping said mechanism and comprising a trip member movable between tripped and untripped positions and biased in the untripped position, a cam on said crank shaft and operable for holding said member in the tripped position when the contacts bounce open in response to an attempt toclose against fault currents that are higher than their ability to close and latch the cam having a step surface engageable with said member when the closing spring means are charged, and latch means being mounted on said member for engagement with the step surface of the cam.

2. The circuit breaker of claim 1 wherein the latch means comprises a pin mounted on said trip member and extending into the path of rotation of the cam.

3. The circuit breaker of claim 2 wherein said member comprises a substantially vertical slot and the pin is slidably movable in the slot.

4. The circuit breaker of claim 3 wherein the pin is movable to a retracted position in the slot when the closing spring means are being charged.

5. The circuit breaker of claim 2 wherein the member moves the trip rod to the tripped position when the step surface engages the pin. 

1. A circuit breaker comprising a pair of contacts operable between open and closed positions, a circuit breaker mechanism releasable to effect opening of said contacts, a trip structure for latching the circuit breaker mechanism in the closed position and for releasing said circuit breaker mechanism, said trip structure comprising a trip shaft operatively connected to said circuit breaker mechanism, a crank shaft structure operable to close said pair of contacts, closing spring means connected to said crank shaft structure, manual trip means operatively connected to said trip shaft for tripping said mechanism and comprising a trip member movable between tripped and untripped positions and biased in the untripped position, a cam on said crank shaft and operable for holding said member in the tripped position when the contacts bounce open in response to an attempt to close against fault currents that are higher than their ability to close and latch the cam having a step surface engageable with said member when the closing spring means are charged, and latch means being mounted on said member for engagement with the step surface of the cam.
 2. The circuit breaker of claim 1 wherein the latch means comprises a pin mounted on said trip member and extending into the path of rotation of the cam.
 3. The circuit breaker of claim 2 wherein said member comprises a substantially vertical slot and the pin is slidably movable in the slot.
 4. The circuit breaker of claim 3 wherein the pin is movable to a retracted position in the slot when the closing spring means are being charged.
 5. The circuit breaker of claim 2 wherein the member moves the trip rod to the tripped position when the step surface engages the pin. 